The invention relates to polymer-bonded pencil leads for writing, drawing, and/or painting devices.
The principle of pencil leads of such kind for writing, drawing, and/or painting is known. Polymer-bonded, graphite-based pencil leads for writing, drawing, and/or painting are understood to be leads that are solidly embedded in wood or other materials that are capable of being sharpened, and also leads that are retained in sliding manner inside a rigid enclosure. Examples of such are wood-encased pencils and pencil leads for mechanical pencils, also known as propelling pencils or clutch pencils, for example. In this context, the pencil leads usually have an outer diameter from about 0.3 mm to 6 mm.
Thus for example, polymer-bonded graphite pencil leads are known from German Patent No. DE 38 27 968 C1. Unfired pencil leads of this kind contain a polymer binder, lubricant and filler materials.
One of the problems in producing such leads is that with a high filler content of greater than 50% by weight, the writing and painting properties of such articles are very good, but the viscosity of the lead paste during extrusion is extremely high, and the extrusion pressure required in the tool and the extruder assumes very large values. The head pressure is about 350 bar. The effect of this is disadvantageous in that the extruder must be larger, and complex equipment must be used. The service life of the machines and tools is also significantly shortened by the high extrusion pressure.